The present invention is related to switching regulators. More particularly, the present invention is related to systems and methods for applying current-mode feedback to a switching regulator.
A switching regulator switches between two voltage points at a frequency that dictates an average output voltage. In some cases, the switching may be accomplished through use of a timer circuit that implements a constant frequency switching characteristic. In such cases, a current-mode feedback is not used, however, such timer based switching often occurs at a much slower rate than that achievable through the use of feedback circuitry reducing the efficiency of the regulator circuit. Further, in such cases, the switching must account for any load capacitance which is undesirable. Accounting for output capacitance, among other things, can result in relatively complex circuitry.
In part because of the aforementioned limitations, some switching regulator circuits include a feedback circuit that controls at least a portion of the switching. For example, in a hysteretic type regulator, a switching frequency will be determined by an external capacitor or other added resistance. A voltage drop across the external resistor is used to determine a current traversing the resistor. This current is fed back to the switching regulator, and the switching regulator in turn uses the feedback to guide switching processes. FIG. 1 shows a regulator output circuit 100 including such an external resistor 110. A node 140 connects external resistor 110 to a driving regulator circuit (not shown), and to a load 130 being driven by the regulator circuit. A capacitor 120 is in series with external resistor 110.
While external resistor 110 may alleviate the problems mentioned above in relation to the fixed frequency switching circuit, it introduces additional problems. For example, external resistor 110 may require additional cost and board space, and in any event external resistor 110 dissipates power during operation of the switching regulator. Further, a larger ripple is exhibited at node 140 when external resistor 110 is used. Alternatively, if the output is taken at a node 150, external resistor 110 directly contributes to output impedance which is undesirable in a regulator circuit.
Hence, for at least the aforementioned reasons, there exists a need in the art for advanced systems and methods for providing feedback in switching regulator circuits.